From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: X-Spam-Checker-Version: SpamAssassin 3.4.0 (2014-02-07) on aws-us-west-2-korg-lkml-1.web.codeaurora.org X-Spam-Level: X-Spam-Status: No, score=-6.8 required=3.0 tests=DKIMWL_WL_HIGH,DKIM_SIGNED, DKIM_VALID,HEADER_FROM_DIFFERENT_DOMAINS,MAILING_LIST_MULTI,SIGNED_OFF_BY, SPF_HELO_NONE,SPF_PASS,USER_AGENT_GIT autolearn=unavailable autolearn_force=no version=3.4.0 Received: from mail.kernel.org (mail.kernel.org [198.145.29.99]) by smtp.lore.kernel.org (Postfix) with ESMTP id BB5A1C2BBC7 for ; Sat, 11 Apr 2020 12:19:04 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [209.132.180.67]) by mail.kernel.org (Postfix) with ESMTP id 9221320787 for ; Sat, 11 Apr 2020 12:19:04 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/simple; d=kernel.org; s=default; t=1586607544; bh=PhTBQGe34MIRkWGZEf+e2K3WKKmuKQ2H5sQ2gRwNrR0=; h=From:To:Cc:Subject:Date:In-Reply-To:References:List-ID:From; b=mVI4F6qA5Taqm2uGOQ+i1BA+0wuG7EHCOgPxq179iWMJniYLQ5Ooj8ym2WvmatRnQ uzeTrX3nOMtZd27c/mpy+exZ1GBSKqPfUAOlrlUvDYR4ml2VTPFHdn/W+3X2RS7SX2 1B9nninUyI2UX6WRDjTNBj07W1QfN1FlmAp6AJXM= Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1728720AbgDKMTC (ORCPT ); Sat, 11 Apr 2020 08:19:02 -0400 Received: from mail.kernel.org ([198.145.29.99]:54172 "EHLO mail.kernel.org" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1728341AbgDKMTA (ORCPT ); Sat, 11 Apr 2020 08:19:00 -0400 Received: from localhost (83-86-89-107.cable.dynamic.v4.ziggo.nl [83.86.89.107]) (using TLSv1.2 with cipher ECDHE-RSA-AES256-GCM-SHA384 (256/256 bits)) (No client certificate requested) by mail.kernel.org (Postfix) with ESMTPSA id 2806E20787; Sat, 11 Apr 2020 12:18:59 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/simple; d=kernel.org; s=default; t=1586607539; bh=PhTBQGe34MIRkWGZEf+e2K3WKKmuKQ2H5sQ2gRwNrR0=; h=From:To:Cc:Subject:Date:In-Reply-To:References:From; b=UdLlorKB3NXlmQPdYGPukpL4PDiAWYRQdLsfxMPn8GuUHP3lzin5395KWVzlCYF2E COWoDgw+LU3sVfyf4RfsPZ9Z6UTyNax+8MHGM4d/Q0taYqpitlqloJudnM3nFrL6ip QUD3pP2g7Owx9kdnMbWqnhj1PmJJfIxxpl04H3kg= From: Greg Kroah-Hartman To: linux-kernel@vger.kernel.org Cc: Greg Kroah-Hartman , stable@vger.kernel.org, Silvio Cesare , Kees Cook , Andrew Morton , Christoph Lameter , Pekka Enberg , David Rientjes , Joonsoo Kim , Linus Torvalds Subject: [PATCH 5.5 20/44] slub: improve bit diffusion for freelist ptr obfuscation Date: Sat, 11 Apr 2020 14:09:40 +0200 Message-Id: <20200411115458.744487200@linuxfoundation.org> X-Mailer: git-send-email 2.26.0 In-Reply-To: <20200411115456.934174282@linuxfoundation.org> References: <20200411115456.934174282@linuxfoundation.org> User-Agent: quilt/0.66 MIME-Version: 1.0 Content-Type: text/plain; charset=UTF-8 Content-Transfer-Encoding: 8bit Sender: linux-kernel-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org From: Kees Cook commit 1ad53d9fa3f6168ebcf48a50e08b170432da2257 upstream. Under CONFIG_SLAB_FREELIST_HARDENED=y, the obfuscation was relatively weak in that the ptr and ptr address were usually so close that the first XOR would result in an almost entirely 0-byte value[1], leaving most of the "secret" number ultimately being stored after the third XOR. A single blind memory content exposure of the freelist was generally sufficient to learn the secret. Add a swab() call to mix bits a little more. This is a cheap way (1 cycle) to make attacks need more than a single exposure to learn the secret (or to know _where_ the exposure is in memory). kmalloc-32 freelist walk, before: ptr ptr_addr stored value secret ffff90c22e019020@ffff90c22e019000 is 86528eb656b3b5bd (86528eb656b3b59d) ffff90c22e019040@ffff90c22e019020 is 86528eb656b3b5fd (86528eb656b3b59d) ffff90c22e019060@ffff90c22e019040 is 86528eb656b3b5bd (86528eb656b3b59d) ffff90c22e019080@ffff90c22e019060 is 86528eb656b3b57d (86528eb656b3b59d) ffff90c22e0190a0@ffff90c22e019080 is 86528eb656b3b5bd (86528eb656b3b59d) ... after: ptr ptr_addr stored value secret ffff9eed6e019020@ffff9eed6e019000 is 793d1135d52cda42 (86528eb656b3b59d) ffff9eed6e019040@ffff9eed6e019020 is 593d1135d52cda22 (86528eb656b3b59d) ffff9eed6e019060@ffff9eed6e019040 is 393d1135d52cda02 (86528eb656b3b59d) ffff9eed6e019080@ffff9eed6e019060 is 193d1135d52cdae2 (86528eb656b3b59d) ffff9eed6e0190a0@ffff9eed6e019080 is f93d1135d52cdac2 (86528eb656b3b59d) [1] https://blog.infosectcbr.com.au/2020/03/weaknesses-in-linux-kernel-heap.html Fixes: 2482ddec670f ("mm: add SLUB free list pointer obfuscation") Reported-by: Silvio Cesare Signed-off-by: Kees Cook Signed-off-by: Andrew Morton Cc: Christoph Lameter Cc: Pekka Enberg Cc: David Rientjes Cc: Joonsoo Kim Cc: Link: http://lkml.kernel.org/r/202003051623.AF4F8CB@keescook Signed-off-by: Linus Torvalds Signed-off-by: Greg Kroah-Hartman --- mm/slub.c | 2 +- 1 file changed, 1 insertion(+), 1 deletion(-) --- a/mm/slub.c +++ b/mm/slub.c @@ -259,7 +259,7 @@ static inline void *freelist_ptr(const s * freepointer to be restored incorrectly. */ return (void *)((unsigned long)ptr ^ s->random ^ - (unsigned long)kasan_reset_tag((void *)ptr_addr)); + swab((unsigned long)kasan_reset_tag((void *)ptr_addr))); #else return ptr; #endif